1. Field of the Invention
The present invention relates to a Liquid-Crystal Display (LCD) and more particularly, to an active-matrix addressing LCD panel including a Thin-Film Transistor (TFT)-array substrate, and a method of repairing any breaking or disconnection in the source/drain bus lines arranged on the TFT-array substrate.
2. Description of the Prior Art
A TFT-array substrate of an LCD panel has a large number of TFTs, a large number of bus lines for the TFTs, and their relating components or members. However, only one of the TFTs and its neighboring bus lines and components or members are explained in this specification and or drawings attached for the sake of simplification of description.
A conventional method of fabricating a TFT-array substrate of an LCD panel is shown in FIGS. 1A to 1D.
First, a metal layer (not shown), which is typically made of a metal such as chromium (Cr), molybdenum (Mo), or aluminum (Al), or their alloy, is formed on a glass plate 102 to have a thickness of several hundreds nanometers. A photoresist is coated on the metal layer thus formed by spin coating, thereby forming a photoresist layer (not shown) on the metal layer.
The photoresist layer is exposed selectively to light using a mask (not shown) with a specific pattern and then, is developed using an alkaline aqueous solution. This, the pattern on the mask is transferred onto the photoresist layer.
Subsequently, using the patterned photoresist layer as a mask, the underlying metal layer is selectively etched to form a gate bus line 110, a rectangular gate electrode 111, and rectangular light-shielding layers 150 and 151 on the glass plate 102, as shown in FIG. 1A.
The gate electrode 111 is formed to be integrated with the gate bus line 110. The light-shielding layer 150 and 151, which are located apart from each other, are separated from the gate bus line 110. After the etching process is completed, the patterned photoresist layer is removed.
The light-shielding layers 150 and 151 are provided on the TFT-array substrate for the purpose of increasing the aperture ratio of the LCD panel.
Further, an insulating layer (not shown) with a thickness of several hundreds nanometers is deposited on the glass plate 102 to cover the gate bus line 110, the gate electrode 111, and the light-shielding layers 150 and 151 by Chemical Vapor Deposition (CVD). A part of the insulating layer, which overlaps with the underlying gate electrode 111, serves as a gate insulating layer of a TFT Tr.
An amorphous silicon (Si) layer (not shown) with a thickness of several hundreds nanometers is formed on the insulating layer thus deposited by a CVD process. The amorphous silicon layer is then patterned to form a semiconductor island 130. The amorphous silicon layer is entirely overlapped with the underlying gate electrode 111, as shown in FIG. 1B.
Using the same way as that in the previous step of forming the gate bus line 110, a drain bus line 120 and a rectangular drain electrode 126 are formed on the insulating layer by a patterned metal layer with a thickness of several hundreds nanometers, as shown in FIG. 1C. The drain bus line 120 extends perpendicular to the gate bus line 110 and runs through the space between the light-shielding layers 150 and 151. The drain bus line 120 is partially overlapped with the underlying light-shielding layers 150 and 151 through the insulating layer.
The drain electrode 126 is formed to be integrated with the drain bus line 120 in the vicinity of the intersection of the gate and drain bus lines 110 and 120. The drain electrode 126 is overlapped with the underlying gate electrode 111 through the insulating layer. The end of the drain electrode 126 is contacted with the semiconductor island 130.
A transparent, conductive layer (not shown) with a thickness of several tens nanometers, which is made of Indium Tin Oxide (ITO) or the like, is deposited on the insulating layer by sputtering. The transparent, conductive layer is patterned by photolithography and etching to form a transparent pixel electrode 140 and a source electrode 141 on the insulating layer, as shown in FIG. 1D. The pixel electrode 140 is partially overlapped with the underlying light-shielding layer 150 through the insulating layer. The pixel electrode 140 is located in a pixel area defined by the adjoining two gate bus lines 110 and the adjoining two drain bus lines 120 so as to be apart from these gate bus lines 110 and these drain bus lines 120.
The source electrode 141 is formed to be integrated with the pixel electrode 140 in the vicinity of the intersection of the gate and drain bus lines 110 and 120. The source electrode 141 is overlapped with the underlying gate electrode 111 through the insulating layer. The end of the source electrode 141 is contacted with the semiconductor island 130.
The TFT Tr is formed by the gate electrode 111, the gate insulating layer, the drain electrode 126, and the source electrode 141.
The TFT-array substrate thus fabricated is then coupled with a color-filter substrate (not shown) so as to make a fixed small gap therebetween. A liquid crystal is then filled in the gap. Thus, the LCD panel is finished.
Fabrication yield improvement is the most important problem to be solved in LCD fabrication. The fabrication yield tends to decrease due to various causes. xe2x80x9cBus-line breaking or disconnectionxe2x80x9d, which is a typical one of the causes, gives a large effect to the fabrication yield because only one bus-line breaking or disconnection occurring in a LCD panel leads to a xe2x80x9cline defectxe2x80x9d, making the whole LCD panel defective.
Accordingly, to reduce the percent defective due to bus-line breaking, a lot of improved structures have been developed.
An improved structure is disclosed in the Japanese Non-Examined Patent Publication No. 5-19294 published in January 1993, which is schematically shown in FIG. 2. In FIG. 2, the same reference numerals as those in FIGS. 1A to 1D are attached to the corresponding elements and therefore, the description relating to the same or corresponding elements is omitted here for simplification.
As shown in FIG. 2, in the same level as that of the gate bus line 110 and the protruding gate electrode 111, a first conductive layer 112 with a rectangular shape is formed on the glass substrate 102 to be apart from the gate bus line 110. The first conductive layer 112 is located at a position to be partially overlapped with the overlying pixel electrode 140.
In the same level as that of the drain bus line 120 and the protruding drain electrode 126, a protruding part 125 with a rectangular shape is formed on the insulating layer to be integrated with the drain bus line 120. Further, a second conductive layer 127 with a rectangular shape and a source electrode 128 with a rectangular shape are formed on the insulating layer in the level of the drain bus line 120. The second conductive layer 127 is located at a position to be partially overlapped with the underlying first conductive layer 112 and the overlying pixel electrode 140. The source electrode 128 is contacted with the underlying semiconductor island 130 and the overlying pixel electrode 140.
If a breaking or disconnection 60 occurs in the drain bus line 120, a laser beam is irradiated to (a) an overlapped area 170 of the protruding part 125 of the line 120 with the underlying first conductive layer 112, (b) an overlapped area 171 of the second conductive layer 127 with the underlying first conductive layer 112 and the overlying pixel electrode 140, (c) an overlapped area 172 of the drain electrode 126 with the underlying gate electrode 111, (d) an overlapped area 173 of the source electrode 128 with the underlying gate electrode 111, respectively. Thus, the upper and lower layers or regions are electrically connected to each other at the overlapped areas 170, 171, 172, and 173, respectively.
In the same step as that of the above laser-beam irradiation, a laser beam is further irradiated to an area 174 located at the bottom of the gate electrode 111, thereby separating the gate electrode 111 from the gate bus line 110. As a result, a part of the drain bus line 120 is electrically connected to the pixel electrode 140 through the protruding part 125, the first and second conductive layers 112 and 127, and another part of the drain bus line 120 is electrically connected to the pixel electrode 140 through the drain electrode 126, the gate electrode 111, and the source electrode 128. This means that the broken or disconnected drain bus line 120 due to the breaking 60 is bypassed through the pixel electrode 140.
With the improved structure of the LCD panel disclosed in the Japanese Non-Examined Patent Publication No. 5-19294, however, an electric current flows from the broken drain bus line 120 to the pixel electrode 140. Therefore, the pixel corresponding to this pixel electrode 140 will form a bright dot, resulting in a point defect.
This means that the improved structure in the Japanese Non-Examined Patent Publication No. 5-19294 is not prudential for breaking or disconnection repairing.
Anther improved structure is disclosed in the Japanese Non-Examined Patent Publication No. 5-5896 published in January 1993. In this structure, first and second conductive regions are formed on the glass plate, which is in the level of the gate bus line. The first and second conductive regions are located at each side of the gate bus line in the vicinity f the intersection of the gate and drain bus lines. is In the level of the drain bus line, first and second protruding parts of the drain bus line are formed on the insulating layer to be overlapped with the underlying first and second conductive regions, respectively. A third conductive region is formed on the insulating layer in the vicinity of the intersection of the gate and drain bus lines. The third conductive region extends along the drain bus line from the first conductive region to the second conductive region. The third conductive region are overlapped with the underlying first and second conductive regions, respectively.
Thus, a redundant structure formed by the first to third conductive regions is provided near the intersection of the gate and drain bus lines.
If a breaking occurs in the drain bus line near the intersection, a laser beam is irradiated to the overlapped areas of the first and second protruding parts of the drain bus line with the underlying first and second conductive regions, and the overlapped areas of the third conductive region with the underlying first and second conductive regions, respectively. As a result, the broken or disconnected drain bus line is bypassed through the first, second, and third conductive regions.
With the improved structure of the LCD panel in the Japanese Non-Examined Patent Publication No. 5-5896, however, this structure cannot cope with any breaking or disconnection occurring at the locations far away from the gate bus line.
Also, when a breaking occurs in the drain bus line, the redundant structure, which is located near the breaking portion in the same level as that of the drain bus line, tends to be broken. Therefore, this redundant structure is not prudential for breaking repairing.
Further, this redundant structure causes some reduction in aperture ratio and consequently, it will degrade the display characteristics.
Still anther improved structure is disclosed in the Japanese Non-Examined Patent Publication No. 4-283725 published in October 1992. In this structure, a conductive region is formed to be entirely overlapped with the gate or drain bus line through the insulating layer as a redundant structure.
If a breaking or disconnection occurs in the gate or drain bus line at a location overlapping with the redundant structure, a laser beam is irradiated to the overlapped areas of the gate or drain bus line with the redundant conductive region, thereby electrically reconnecting the broken gate or drain bus line through the conductive region. Thus, a line defect can be repaired.
With the improved structure of the LCD panel in the Japanese Non-Examined Patent Publication No. 4-283725, however, the light-shielding layers cannot be formed on the TFT-array substrate by the same metal layer as that for the gate bus line due to this redundant structure. This decreases the aperture ratio, because a black matrix serving as the light-shielding layer needs to be formed on a color-filter substrate with sufficiently large margins corresponding to the possibly overlay accuracy of the color-filter substrate with the TFT-array substrate.
Accordingly, an object of the present invention is to provide an LCD panel in which a bypass can be readily formed for a broken or disconnected one of the source/drain bus lines without degrading any display characteristic and without increasing the number of man-hour.
Another object of the present invention is to provide an LCD panel having a high repairing capability.
Still another object of the present invention is to provide a repair method of an LCD panel in which a broken or disconnected one of the source/drain bus lines is repaired without degrading any display characteristic and with high repairing capability.
A further object of the present invention is to provide an LCD panel and a repair method thereof that raises the fabrication yield of an LCD panel.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, an LCD panel is provided, which includes a TFT-array substrate.
The TFT-array substrate has a plate, gate bus lines formed on the plate to extend along a first direction, source/drain bus lines formed on the plate to extend along a second direction perpendicular to the first direction, pixel areas formed on the plate and defined by the gate bus lines and the source/drain bus lines, TFTs formed near respective intersections of the gate bus lines and the source/drain bus lines in the corresponding pixel areas, pixel electrodes formed in the respective pixel areas, and light-shielding layers formed in the respective pixel areas.
Each of the TFTs has a gate electrode electrically connected to a corresponding one of the gate bus lines, a pair of source/drain electrodes electrically connected to a corresponding one of the source/drain bus lines and a corresponding one of the pixel electrodes, respectively.
Each of the source/drain bus lines is overlapped with a corresponding one of the light-shielding layers at first and second locations. The first and second location are defined in such a way that a bypass for each of the source/drain bus lines is formed by electrically connecting each of the source/drain bus lines to the corresponding one of the light-shielding layers at the associated first and second locations.
With the LCD panel according to the first aspect of the present invention, each of the source/drain bus lines is overlapped with a corresponding one of the light-shielding layers at first and second locations. The first and second locations are defined in such a way that a bypass for each of the source/drain bus lines is formed by electrically connection each of the source/drain bus lines to the corresponding one of the light-shielding layers at the associated first and second locations.
Accordingly, when a breaking or disconnection occurs in any one of the source/drain bus lines, the broken one of the source/drain bus lines is electrically reconnected through the bypass formed by electrically connecting the broken one of the source/drain bus lines to a corresponding one of the light-shielding layers at the corresponding ones of the first and second locations. This means that a bypass can be readily formed for the broken or disconnected one of the source/drain bus lines.
Also, the light-shielding layers may be formed in the same process as that of forming the gate bus lines. The first and second locations for each of the source/drain bus lines may be formed by simply changing a mask pattern for the source/drain bus lines. Therefore, the number of man-hour is not increased.
Further, since the bypass for the broken one of the source/drain bus lines is formed by using the corresponding one of the light-shielding layers, the light-shielded area of each of the pixel areas is not increased. The light-shielding layers are located in the respective pixel areas on the TFT-array substrate. As a result, the aperture ratio may be kept high. In other words, no degradation occurs in any display characteristic.
Additionally, the bypass can be formed even if a breaking or disconnection occurs at a location far from the intersections of the gate and source/drain bus lines. This means that a high repairing capability is realized.
As a result, because of the above-described reasons, the LCD panel according to the first aspect raises the fabrication yield of an LCD panel.
In a preferred embodiment of the LCD panel according to the first aspect, each of the source/drain bus lines has first and second protruding parts for each of the pixel areas. The first and second protruding parts of each of the source/drain bus lines are formed to laterally protrude from a same side of a corresponding one of the source/drain bus lines to be overlapped with a corresponding one of the light-shielding layers.
The first and second locations are positioned in the first and second protruding parts of each of the source/drain bus lines in a corresponding one of the pixel areas, respectively.
In another preferred embodiment of the LCD panel according to the first aspect, each of the light-shielding layers has first and second protruding parts. The first and second protruding parts of each of the light-shielding layers are formed to laterally protrude from a same side of a corresponding one of the light-shielding layers to be overlapped with a corresponding one of the source/drain bus lines.
The first and second locations are positioned in the first and second protruding parts of each of the light-shielding layers, respectively.
In this case, it is preferred that adjacent two ones of the light-shielding layers for each of the source/drain bus lines are mechanically connected to each other at a location below a corresponding one of the source/drain bus lines.
According to a second aspect of the present invention, a repair method of an LCD panel is provided. The LCD panel includes a TFT-array substrate having the following structure.
The TFT-array substrate has a plate, gate bus lines formed on the plate to extend along a first direction, source/drain bus lines formed on the plate to extend along a second direction perpendicular to the first direction, pixel areas formed on the plate and defined by the gate bus lines and the source/drain bus lines, TFTs formed near respective intersections of the gate bus lines and the source/drain bus lines in the corresponding pixel areas, pixel electrodes formed in the respective pixel areas, and light-shielding layers formed in the respective pixel areas.
Each of the TFTs has a gate electrode electrically connected to a corresponding one of the gate bus lines, a pair of source/drain electrodes electrically connected to a corresponding one of the source/drain bus lines and a corresponding one of the pixel electrodes, respectively.
Each of the source/drain bus lines is overlapped with a corresponding one of the light-shielding layers at first and second locations. The first and second locations are defined in such a way that a bypass for each of the source/drain bus lines is formed by electrically connecting each of the source/drain bus lines to the corresponding one of the light-shielding layers at the associated first and second locations.
The repair method of and LCD according to the second aspect of the present invention has a step of irradiating a laser beam to the first and second locations of a broken or disconnected one of the source/drain bus lines and a corresponding one of the light-shielding layers, thereby forming a bypass for the broken one of the source/drain bus lines with the use of the corresponding one of the light-shielding layers.
With the repair method of and LCD according to the second aspect of the present invention, because of the same reason as that in the LCD panel according to the first aspect, the broken one of the source/drain bus lines is repaired without degrading any display characteristic and with high repairing capability.
As a result, the repair method according to the second aspect raises the fabrication yield of an LCD panel.